1. Field of the Invention
The present invention relates to a liquid applying apparatus and an ink-jet printing apparatus. More specifically, the present invention relates to a liquid applying apparatus for coating a medium with a liquid for a predetermined purpose such as facilitating coagulation of pigments when ink-jet printing with ink having the pigments as color material or the like. Also, the present invention relates to an ink-jet printing apparatus provided with a mechanism for applying a liquid to a printing medium for a purpose of facilitating coagulation of pigments at printing with ink having the pigments as color material.
2. Description of the Related Art
As a method for widely applying a liquid or a liquid material to a medium, a spin coater, a roll coater, a bar coater and a die coater are known. These coating methods assume continuous coating on a coating medium with a relatively long length in the conveying direction. Therefore, for example, if a coating medium with a relatively small size is intermittently conveyed for coating, a problem might occur that a uniform coated film can not be obtained because a coating bead is disturbed at the coating start or end position of each coating medium.
As a configuration to solve the above problem, an apparatus described in Japanese Patent Application Laid-open No. 2001-070858 is known. In this configuration, a rotating rod bar is used in the dye coater method to discharge paint from a discharge slit to the rod bar and form a coated film on the rod bar. Then, the formed coated film comes in contact with a coating medium so that the coated film is transferred to the coating medium with rotation of the rod bar. When the coated film formed on the rod bar is not transferred to coat the coating medium, the paint is returned into a head by rotation of the rod bar and recovered through a collection slit. That is, the rod bar keeps on rotating even if a coating operation is not performed, and at that time, the paint is in the state forming a coated film on the rod bar. By this, even if the coating medium is supplied intermittently and coating is performed on them intermittently, uniform coated films can be obtained.
A device using a liquid applying mechanism is also known in a field of an ink-jet printing apparatus. Japanese Patent Application Laid-open No. 2002-517341 discloses use of a doctor blade in contact with a roller so that a coating liquid is recovered between this blade and the roller and the coating liquid is applied to this roller in response to rotation of the roller. And in response to the rotation of the roller, the coating liquid applied to the roller is transferred to be applied to a support body conveyed between this and another rollers. Japanese Patent Application Laid-open No. 8-072227 (1996) also discloses a mechanism in an ink-jet printing apparatus for applying a treatment liquid to insolubilize a dye in advance before printing. An embodiment 1 of this document describes that the treatment liquid in a replenishment tank is drawn out by attached to a rotating roller and at the same time, the drawn treatment liquid is applied to a printing paper.
However, in any of the configurations described in the above Japanese Patent Application Laid-open No. 2001-070858, Japanese Patent Application Laid-open No. 2002-517341, and Japanese Patent Application Laid-open No. 8-072227 (1996), a coating liquid is applied or supplied to the surface of a bar or a roller while the rod bar or the roller is rotating, and a portion to which the coating liquid is applied is open to or communicates with the atmosphere. Therefore, vaporization of the coating liquid may cause a problem and when the attitude of the apparatus is changed, that might cause a problem of leakage of the coating liquid. Particularly, in an ink-jet printing device as a printer, considering leakage of a liquid due to attitude change during transportation, the coating mechanisms described in the above each document are hard to be employed to a small-sized apparatus.
On the other hand, a configuration that a portion of a roller to which an ink as a coating liquid is applied or supplied is sealed is disclosed in Japanese Patent Application Laid-open No. 8-058069 (1996). The coating mechanism described in this document is a mechanism for applying ink to a roller having a surface on which a pattern of a printing plate is formed in a gravure printing device. Here, a chamber member is used having doctor blades extending in the longitudinal direction of the roller at positions corresponding to upper and lower two locations along a circumferential surface of the roller and elastic members provided respectively at both ends of these two doctor blades. By bringing the chamber member into contact with the circumferential surface of the roller, a liquid chamber is formed between the chamber member and the roller. And when the roller is rotated, the coating liquid in the liquid chamber is applied or supplied to the roller.
In the coating apparatuses as described in the above Japanese Patent Application Laid-open No. 2001-070858, Japanese Patent Application Laid-open No. 2002-517341, Japanese Patent Application Laid-open No. 8-072227 (1996) and Japanese Patent Application Laid-open No. 8-058069 (1996), a problem might occur which is caused by that the liquid for coating is kept at a certain location in the apparatus and does not flow for a relatively long time. For example, if a coating operation is not performed for a relatively long time, the coating liquid remaining on the surface of the coating roller may become thick, and thus when the coating operation start again, the roller may not rotate normally or a medium can not be coated uniformly with the liquid.
For these problems, Japanese Patent Application Laid-open No. 2002-096452 describes that coating initial process, which is an operation to rotate a coating roller without a medium at a power on the apparatus or every predetermined time during standby for a printing operation in the printing apparatus employing a coating liquid. More specifically, when the coating roller is rotated without the medium, the coating liquid attached to the coating roller is refreshed, and thus viscosity of the coating liquid on the coating roller can be lowered. In this way, according to Japanese Patent Application Laid-open No. 2002-096452, even if the coating liquid on the coating roller has had high viscosity, the viscosity can be lowered or the coating liquid of increased viscosity can be eliminated, which enables the subsequent coating operation to be performed well.
However, in the Japanese Patent Application Laid-open No. 2002-096452, aviscosity increase of the coating liquid on the coating roller is recognized as a problem, but a viscosity increase of the coating liquid in a flow path for supplying the coating liquid to the coating roller is not recognized as a problem. More specifically, in a form for supplying the coating liquid from a reservoir tank of the coating liquid to the coating roller via the flow path, the coating liquid in the flow path is evaporated when a non-operating state lasts for a long time, and thus the coating liquid becomes high viscous or is fixed, in the flow path. In order to reduce this viscosity increase or fixation, it is desirable to recover the coating liquid from the flow path before the non-operating state lasts for a long time. However, Japanese Patent Application Laid-open No. 2002-096452 does not describe such a recovering operation of the coating liquid. Moreover, Japanese Patent Application Laid-open No. 2001-070858, Japanese Patent Application Laid-open No. 2002-517341, Japanese Patent Application Laid-open No. 8-072227 (1996) and Japanese Patent Application Laid-open No. 8-058069 (1996) do not describe the recovering of the coating liquid before the non-operating state lasts for a long-time, either.
If the coating liquid can be surely recovered before the non-operating state lasts for a long time, the problem of the viscosity increase or the fixation of the coating liquid in the flow path does not become apparent. However, in the case of unintentional stop of operations of an apparatus due to outage or the like, the apparatus is powered off without performing the above recovering operation. In this case, the coating liquid remains in the flow path for a long time, and the remaining coating liquid may cause the viscosity increase or the fixation in the flow path. Because of this, in some cases the subsequent coating operation can not be performed well.
Also, the problem of the viscosity increase or the fixation when the recovering operation is not performed does not occur only in the flow path. If the recovering operation is not performed, the liquid is left in contact with the coating roller for a long time. As a result, the viscosity increase or the fixation of the liquid will occur on the surface of the coating roller and cause a problem of uneven coating or the like.